Surface Fasteners of the Slidingly Engagable type (SEFs) were disclosed in U.S. Pat. No. 5,983,467 entitled “Interlocking Device” by the undersigned. That disclosure included a range of fastener types, each including portions with a base structure having pluralities of apertures and islands, which may be slidingly engaged by application of a relative shearing force, so that the individual islands of one portion become interlocked within complementary apertures of the other, and vice versa. SEFs may be provided in various designs including uni-directional or multi-directional orientations; may be hermaphroditic or have different male and female portions; may be configured to connect a point, an edge, a strap, a surface or other condition; may include an associated aperture opening that provides a “snap fit” prior to engagement, and may also include diverse self-alignment and coupling mechanisms.
Typically, the individual apertures of Slidingly Engagable Fasteners are designed to receive complementary islands so as to allow a relatively loose and imprecise initial alignment to result in a relatively tight and more precise engaged state, after application of a relative shearing force. Three characteristics define this aspect. First, the apertures and complementary islands are effectively tapered in at least one dimension in relation to the axis of engagement so as to provide an aperture opening that is somewhat larger in at least one dimension than the leading edge of an associated island, thereby abetting self-alignment of the elements. Secondly, each such aperture includes at least one undercut wall segment which, after application of the relative shearing force (i.e. a force applied to one of the portions in a direction generally parallel with the basal surface) to the aligned portions, engages a complementary island undercut sidewall segment so as to contain the island and prevent further movement in a direction generally perpendicular to the basal surface (vertical). Thirdly, each such aperture also includes wall segments which, upon application of the relative shearing force, engage complementary island sidewall segments so as to contain such island and prevent further movement in the direction of such applied shearing force (engagement direction) or in a direction generally perpendicular to such force and also parallel with the basal surface (lateral direction). The term “slidingly engaged” is intended to convey that the islands are caused (by the relative shearing force) to enter complementary apertures so that the island sidewalls progressively approach aperture walls until reaching a state of full contact and engagement, in which state the portions are effectively interlocked.
The profile shape of such walls and sidewalls (as viewed in cross section perpendicular to the axis of engagement), as illustrated in U.S. Pat. No. 5,983,467 include orthogonal dovetail-like shapes, ogee-like shapes, and variations of such shapes. It is apparent that any profile shape which provides the appropriate engagement and containment aspects as described above may be used. It may also be understood that any such walls or sidewalls need not be contiguous in order to provide such engagement and containment aspects. Therefore it has become known to the present inventor that Slidingly Engagable Fasteners may include elements which are discontinuous, perforated, or otherwise modified in design, provided only that the essential function and structural integrity of the device is maintained. In that a basic engineering design precept entails minimizing resources in order to achieve a particular function, it may therefore be desirable to produce Improved SEFs with such discontinuity, perforations or other modifications in order to minimize such resources. SEFs can provide significant advantages over hook-and-loop, mushroom-type and other surface fasteners, as well as a wide variety of mechanical fastening devices, for many applications. Such advantages include superior shear and tensile strength, low profile, ease of use, durability, a non-grabbing texture, and numerous other aspects. However, in order to advantageously provide these advantages, a simple and economical method of producing SEF fasteners in large or small quantities, in a variety of materials, and in a range of designs is needed.
In addition to the need for an improved method of production, a number of potential improvements to such fasteners are also desirable which may also be related to such method of production. Slidingly Engagable Fasteners should be available in a variety of materials including molded thermoplastics, other moldable materials, paper and paper board, composite and fibrous materials, and in formed metals, plastics and other malleable materials. Flexibility of the overall structure should be combined with structural integrity of individual fastening elements. SEF products should be available in a range of scales for a diversity of applications. Use and disposition of materials should be economical. Low profile and high strength aspects should be maximized. Fastener portions for many potential application environments should be self-cleaning. Self connecting fasteners in strap or linear forms should be available, including double-sided fastener straps and surfaces. Provisions for integrally attaching SEFs to various substrates should be available. SEF portions which may be integrally molded or formed as part of a larger component or product are also needed. Fasteners which combine certain of these aspects as well as other features are also needed.
Working prototypes of SEFs in various embodiments have been produced by molding, machining, forming, constructing, and die cutting diverse materials such as hard and soft plastics, wood, paper and paperboard, foam, sheet metal, ceramic materials, and composite materials. Although these models have generally been functionally successful, the need for a simple and inexpensive method of production is apparent. Molding or forming SEF fastener portions by conventional methods is complicated by the fact that such fasteners include a multiplicity of undercut surfaces. Although conventional molding or forming techniques may be employed to produce various uni-directional SEFs, multi-directional embodiments present a particular challenge. Therefore, a relatively simple method is needed which will provide for the removal of that part of the die or mold which defines the underside of such undercut surfaces without harming, weakening, or comprising the design of the product.
Several known manufacturing processes are applicable to the present invention: injection molding utilizing a reciprocating machine; continuous molding in which a substance is molded between a set of counter rotating rollers, effectively extruding a continuous product; die forming utilizing a reciprocating press; and continuous die forming in which a sheet of material is formed between a set of rotating dies. Each of these processes has been developed extensively over many years, and are not claimed herein except in relation to the present invention. Each such process also involves numerous secondary systems for pressurizing, heating, cooling, lubricating, ejecting product and waste, and other considerations which are beyond the scope of this disclosure. The common aspects of these processes are that each utilize a set of dies or, more commonly, a single die with a corresponding anvil or backing, and an apparatus designed to provide pressure on a raw material in order to produce a product of the desired shape.
Reclosable surface fasteners such as molded hook-and-loop hookstrips and mushroom type fasteners, which also include undercut surface segments, are typically manufactured of molded thermoplastics. Erb U.S. Pat. No. 3,147,528 describes a method of producing hookstrips by reciprocal injection molding. Other methods utilize a continuous web process using a belt or rotary mold. Undercut fastening elements may be formed by a complex mold with internally moving elements i.e. Menzin et al U.S. Pat. No. 3,758,657; they may be directly molded in cavities provided in such a mold and rapidly cooled before forcibly (resiliently) stripping form the mold i.e. Fischer U.S. Pat. No. 4,775,310; or they may be formed in a two step process in which a base with an array of stems is first molded and the stems are subsequently reformed into hooks or mushroom shapes, i.e. Provost et al U.S. Pat. No. 5,953,797. Yet another possible manufacturing method includes a sacrificial mold portion for forming undercuts, i.e. Torigoe et al U.S. Pat. No. 5,242,649. Recently, Kampfer et al U.S. Pat. No. 6,000,160, Miller U.S. Pat. No. 6,054,091, and Parellada et al U.S. Pat. No. 6,248,276, each disclose improved methods of forming fastener elements by the aforementioned two step process. Many other examples provide variations and refinements to similar processes. It appears that the quest for a definitive method of manufacturing fastener products is ongoing.
Utilizing a set of interengaging dies is a known method of manufacturing complex products with under-surfaces, most commonly known in paper and sheet metal stamping at least far back as Hodgson U.S. Pat. No. 299,982 of 1884, but also employed in plastic molding. Methods of producing certain designs of hook-and-loop hookstrips and mushroom type fasteners by utilizing an apparatus which includes a set of bypassing dies are also known. Kaneko U.S. Pat. No. 5,212,853 discloses injection molded surface fastener products that utilize a set of male and female interdigitating dies to form a unique mushroom-type fastener portion, although such method is not claimed. Kaneko's product includes a fastener head on two legs which are flush with the head perimeter, apparently to provide flexibility. His method includes a set of male and female dies with abutment faces, such faces being more or less perpendicular to the product surface structure. Although it is noted that the abutment faces are slightly tapered to facilitate die separation, it would appear that, without further remedy, repetitive use under heat and pressure could cause die seizure or differential movement if anything other than small portions are produced. Like other types of mushroom fasteners, Kaneko's device appears to be limited in potential strength as related to durability under repetitive use. Kayaki U.S. Pat. No. 5,067,210 appears to depend on a similar molding method which is not described. His device appears to require relatively exact positioning in two dimensions, first to align the ribs then to align alternately offset elements. It is apparent that each such fastener has limited application.
Certain other known fasteners also include a fenestrated base structure which could be produced by a method incorporating bypassing dies. Spier, U.S. Pat. No. 4,581,792, describes a press-together surface fastener comprising a plurality of perpendicular tapered projections and complementary receptacles arrayed in alternating rows each surrounded by a contiguous base structure having openings at each such projection and receptacle. Spier's device, however, appears to maintain engagement by friction rather than providing any type of interlock. It requires precise alignment of the portions, and does not appear to provide significant resistance to shear. Cousins, U.S. Pat. No. 4,183,121, and Allan, U.S. Pat. No. 5,640,744, each disclose types of surface fasteners with undercut elements which include portions having a fenestrated base structure, an engagement mechanism which may be effected by a relative shearing force, and in which openings in the fenestrated base structure at least partially align with undersurface segments of individual engagement members. However, each of these fastening devices appear to require considerable precision in aligning the elements both lineally in columns and in angular orientation. The former, Cousins, appears to require consistent pressure along the length of its axis in order to engage all elements simultaneously, and does not provide for excess overlap when adjusted. The latter, Allan, also requires longitudinal alignment ribs to prevent lateral disengagement. Both provide fastening mechanisms which are not adaptable to resist shear forces oriented in more than a single radial direction and have other limitations.
A new manufacturing method for SEFs should include certain desirable aspects. For instance, having a positive means of defining the thickness of a fastener portion throughout its area is particularly important for producing wide products with either reciprocating or rotating molding systems. Provisions for maximizing production speed are also desirable. Providing enhanced surface features for functional, aesthetic, or identification purposes is also desirable. Precise definition of the shape of individual fastening elements is important in controlling the design of strength and release characteristics. Material efficiency, weight, and flexibility should be carefully designed. Strength of individual fastening elements and profile depth require precise control. Speed, simplicity, and economy of production are important considerations as well are tooling costs. Provision of a method by which fastener portions may be readily manufactured in a one-step process as part of a larger primary product would also have significant utility. In summary, there is a need for a simple, efficient, economical, precise, and versatile method of manufacturing Slidingly Engagable Fastening products.